Place chicken in a non-metallic dish and pour over marinade. Cover and marinate in refrigerator for 1 hour (longer for a richer taste). Preheat oven to 180 deg. Celsius Heat butter and oil in a heavy-based fry pan over medium heat. Cook chicken in batches until golden. Remove to a plate.
Add leek, bacon and garlic to pan. Cook, stirring occasionally for about 4 minutes or until leek is tender. Add stock, wine and mushrooms. Bring to the boil. Remove from heat and transfer mixture to an ovenproof dish. Add chicken, cover with foil and bake for 35 minutes. Remove foil and cook for another 10 minutes or until chicken is cooked through.
Meanwhile, steam snow peas until just tender. Place in a serving bowl. Top chicken with chopped parsley and serve immediately.